JPH0628841A - Storage element using chemical reaction - Google Patents

Abstract

PURPOSE:To attain a recording by providing an electrolyte layer between a pair of electrodes while being in contact with those electrodes, thereby using a chemical reaction. CONSTITUTION:An insulating film 3 and an electrolyte later 4 are present between a bit line 1 and a word line 2. Electrodes 1 and 2 are in contact with the electrolyte layer 4 and the isolating film prevents the contact between electrodes 1, 2 at a place except the element. A deposition metal layer 5 generated by an electrolysis is present between the electrode 2 and the electrolyte layer 4. This deposition is dissolved in the layer 4, or moved to the electrode 1 by a reverse current. The presence or absence of the metal corresponds to '0' and '1', and the content is read by the presence or absence of a conduction. Thus, a storage device whose constitution is simple, and whose integration is high can be obtained, and the storage content can be maintained even when a power source is turned off. Also, the content is stable to the magnetism, so that a reading can be attained at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-volatile and rewritable memory element used in electronic computers, word processors, game cartridges and the like.

[0002]

2. Description of the Related Art Conventionally, as a memory element of a computer,
Various types of magnetic tapes, magnetic discs, compact discs, optical discs, etc. have been used, but as semiconductors, ROM (Read only memory), RAM (Ra
ndom access memory). These memories are widely used because they operate quickly and can be miniaturized, but there is a strong demand for higher integration of the memories as the performance of computers increases. For this purpose, it is necessary to minimize the processing size, and due to advances in technology such as processing with X-rays and electron beams and reduction projection, processing accuracy is reduced from micron to sub-micron order, and memory such as tens of megabits is also available. It was prototyped and put on sale.

However, the reduction of the structural unit due to such miniaturization is approaching the limit because the memory element needs to have a certain capacitance. Although these elements have a MOS-FET as a basic structure, biochips and the like have been proposed as a method for measuring integration and miniaturization without being restricted to such a structure, but they have not yet been considered. (For example, "Introduction to VLSI technology for chemical engineers" edited by the Chemical Engineering Association, Baifukan (1989)).

[0004]

A memory element using a MOS-FET has an excellent balance of high speed, size and operability and is used in a wide range of fields, but its performance is approaching its limit as described above. . Although the RAM is easy to rewrite, the stored contents are lost when the power is turned off, and the ROM does not lose the stored contents, but it cannot be rewritten. Even if it is possible, the contents are erased at once. Otherwise there are many things that are not possible. Further, the completely rewritable one has a problem that the circuit becomes complicated and the size becomes large.

An object of the present invention is to eliminate these drawbacks of a memory element using a MOS-FET, and provide a rewritable memory element having a small size and a simple structure.

[0006]

A feature of the storage element of the present invention is that the storage is performed by a chemical change of the element. This chemical change is an electrochemical change caused by an electric current, and includes, for example, metal deposition and dissolution, chemical changes in the membrane due to electrolytic oxidation or reduction, and changes in the electrolyte concentration due to electrolysis of solutes in the electrolyte. .

On the contrary, these chemical changes lead to changes in electrical properties such as electric conductivity and interface voltage of the electrodes and electrolytes or their interfaces, and recording can be read out by measuring these.

The pair of electrodes is made of metal, semiconductor or the like, of which one electrode is preferably metal and the other electrode is preferably semiconductor. As the metal electrode, gold, silver, copper, aluminum, platinum or the like can be used, but silver and copper are preferable because of stability at room temperature and ease of ionization. Further, as the semiconductor electrode, silicon, gallium arsenide, germanium or the like can be used. Of course, in addition to this metal-semiconductor combination, semiconductor-semiconductor combination, metal-
Combinations of metals are also possible. For the latter, recording can be read by utilizing a change in conductivity depending on the presence or absence of an insulating film by combining a material such as aluminum that can form an insulating film by electrolysis.

The electrolyte is in a non-fluid state due to the stability of the device. As such an electrolyte, for example, i) a polymer produced by electrolytic polymerization such as polythiophene or polypyrrole, ii) a system in which a low molecular salt is dispersed in a polymer matrix such as polyoxyethylene, iii) iodide Examples thereof include superionic conductive materials such as silver-silver borate glass.

Examples of the electrolyte polymer of i) include polythiophene, polypyrrole, poly-3-alkylthiophene, polyparaphenylene, polyacetylene, polybenzothiophene, polyphenylene vinylene, polyoxadiazole, and copolymers thereof. Can be mentioned.

As the polymer matrix of ii), in addition to polyoxyethylene, polyalkylene glycol such as polypropylene glycol, polyethyleneimine, polyethylene sulfide, polypropylene sulfide, polytetramethylene sulfide, copolymers of these monomers, and these Examples thereof include copolymers with other monomers.

Furthermore, as the superionic conducting material _{iii), AgI-Ag 2 O} -B 2 O 3, AgI-Ag 4 P 2 O 7, A
_{gBr-Ag 2 O-B 2} O 3, AgCl-Ag 2 O-B
Examples thereof include ₂ O ₃ and RbAg ₄ I ₅ type glass.

In any of these cases, the ions in the electrolyte must include the ions involved in the electrochemical reaction at the electrode. For example, in the case of metal deposition, it is a metal ion to be deposited, and in the case of an oxidation reaction for forming an insulating film, it is an ion containing oxygen such as OH ~, ClO ₂ ~.
Among the above electrolytes, the electrolyte polymer of i) is easy to prepare because it can use the electrode reaction. The polymer matrix of ii) has the advantage that the ions can be selected relatively freely. Further, iii) the superionic conductive glass is excellent in stability and reliability.

As the substrate, various substrates used for ordinary semiconductors such as silicon and ceramics can be used.

As the insulating film used in the memory element of the present invention, an inorganic film such as silicon oxide or silicon nitride is preferable in terms of insulating property and easiness of production. In addition to these, an organic film such as a polyimide film is used. be able to. This insulating film is not essential, and the insulating film can be eliminated by making the electrolyte layer sufficiently large to prevent contact between the electrodes.

[0016]

Since the memory element of the present invention basically comprises a pair of electrodes and an electrolyte layer existing between them, it does not require a complicated pattern and can be further miniaturized as compared with the conventional element.

As described above, by compounding and miniaturizing the memory element, both the electrode and the electrolyte are miniaturized, and it becomes possible to cause a chemical change necessary for reading of the memory with a small current, and the write time. Can be shortened. In addition, these chemical changes are often reversible reactions that return to the original when a reverse current is applied, and therefore these devices can rewrite the stored contents.

Further, since such a memory is made by a chemical change, the contents are not erased even when the power is turned off, and can be semipermanently preserved by taking appropriate measures such as prevention of electrode oxidation.

Disadvantages of these elements are that it takes a long time to write, that the current at the time of reading may alter the stored contents, and that the current may flow around other elements. Is mentioned. But,
As described above, these are improved by the miniaturization of the element, and even if it takes a little time to write, a small current in which a chemical change is negligible is preferable in reading, so that high speed is achieved. Can be read out, and by taking advantage of such characteristics, the frequency of rewriting is low, such as in books and dictionaries, but it is suitable for applications with high frequency of reading.

As for the above, the probability can be reduced by reducing the ratio of the write current and the read current, but it is not perfect when used for a long time. This can be prevented by flowing an opposite current of the same magnitude as that after reading. The bypass current can be eliminated by inserting a diode in one of the electrodes and blocking the reverse current.

As described above, various reactions can be used for this device, and any of them can be used. Among these, the metal deposition reaction on the semiconductor electrode is most suitable. It is possible to carry out the metal deposition reaction reasonably because not only the conductivity of the metal changes greatly by a very small amount of metal deposition, but also the conductivity in one direction is secured even in the state where no metal is deposited. This is because writing and reading can be performed easily and stably.

The following examples will be described according to this reaction, but the present invention is not necessarily limited to this, and the same purpose can be achieved by using various other reactions as described above. Needless to say.

[0023]

1A and 1B show a typical structure of a storage element. In the figure, electrode 1 is a bit line, electrode 2 is a word line,
The insulating film 3 and the electrolyte layer 4 are present between the two. The electrodes 1 and 2 are in contact with the electrolyte layer 4, respectively. The insulating film 3 is for preventing contact between both electrodes except the element, and the electrode 2 is attached to the substrate 6. There is a deposited metal layer 5 generated by electrolysis between the electrode 2 and the electrolyte layer 4, and the deposited metal layer 5 is dissolved in the electrolyte layer 4 or moved to the electrode 1 side by applying a reverse current. The presence or absence of this metal corresponds to 0 or 1, and the content can be read depending on the presence or absence of conduction between both electrodes.

Of course, as a device, in addition to these elements, there are various I / O selectors, row duders, clock generators, column duders, and the like, which is the same as a normal semiconductor memory. It is like a combination of an I / O selector, sense up, row duder, column duder, clock generator and storage element assembly of the present invention.

In the memory element shown in FIGS. 3 and 4, the individual electrolyte layers 4 are made large enough not to come into contact with each other.
The insulating film 3 shown in 2 is omitted. in this case,
Due to the thickness of the electrolyte layer 4, a space is created between the electrodes 1 and 2 to ensure mutual insulation.

Next, an example of a method for manufacturing these elements will be described.
Of course, these are examples and the present invention is not limited to the following description.

FIGS. 5 and 6 show the manufacturing procedure. FIG. 5 is a sectional view taken along the line AA of FIG. 1, and FIG. 6 is a sectional view taken along the line BB of FIG. One electrode 2 is formed on the substrate 6 as shown in i) of these figures. The procedure of this formation may be formation by vapor deposition, sputtering or CVD, and when a semiconductor is used for the substrate 6, a passivation film is formed by photolithography and then a doping agent is diffused, or an electrode is directly formed by ion implantation. You may.

Next, as shown in ii), the insulating film 3 is formed on the entire surface, and a hole is formed in the element portion. Of course, this step can be omitted, as described above. Insulation film 3
May be formed by CVD, sputtering, or by an oxidation reaction such as thermal oxidation or wet oxidation. Further, in the case of an organic film, it can be formed by coating or by photopolymerization or crosslinking after coating. And to cover the whole part of this hole,
The electrolyte layer 4 is formed as in iii). This can be achieved by a method in which sputtering or a melt is uniformly applied and then etching is performed by photolithography, or a polyether having a polymerizable group such as a double bond is applied in a state containing an ionic electrolyte, and light or electron is applied. After cross-linking with a line or the like, the uncross-linked portion may be washed off with a solvent. It can also be formed by electrolytic polymerization. In this case, since the polymer is deposited around the electrode, there is an advantage that patterning is possible without using photolithography.

Finally, the device is completed by connecting the electrolyte layer 4 and forming the electrode 1 as in iv). The electrode 1 is usually formed by vapor deposition or sputtering. In addition, the deposited metal layer 5 shown in FIG. 1 can be formed in advance by vapor deposition or the like. In this case, the electrical characteristics are changed by melting the metal layer by an electrochemical reaction.

When manufacturing the devices by the above-described method, a clock, a selector, a column duder for operating these devices at any time before, during, or after this step are suitable. It is possible to create auxiliary circuits such as. These are generally performed before the insulating film forming step of ii) shown in FIG. 5 or FIG.

The thus-formed chip is assembled by dicing, bonding and packaging in the same manner as other elements. Regarding these, it is possible to carry out with a conventional technique as with a normal semiconductor. However, when the heat resistance of the electrolyte is low, it is necessary to use a resin having a high fluidity for the packaging and cure it at a low temperature.

Next, as an example of using the chip thus manufactured, the electrode 2 is a p-doped silicon electrode,
The electrolyte of the electrolyte layer 4 is a cross-linked polyether containing silver nitrate,
The case where the electrode 1 is a silver electrode will be described. In such an element, the relationship between the voltage V ₁₂ between the electrodes 1 and 2 and the current I ₁₂ flowing between them is as shown by the solid line in FIG. That is, when a positive electrode is added to the electrode 1, a current flows, and metal ions (Ag +) are deposited as Ag on the electrode 2.
However, even if a positive voltage is applied to the electrode 2, almost no current flows. Even if the current slightly flows, a silicon oxide film is formed on the surface of the electrode 2 and the current stops flowing with time. However, in this state, when a positive voltage is applied to V ₁₂ to pass a current, metallic silver is deposited on the surface of the electrode 2, and the voltage-current relationship becomes as indicated by the dotted line. When a positive voltage is applied to the electrode 2 in this state, a current flows. Therefore, the contents of the memory can be retrieved by applying a positive voltage to the electrode 2 and checking the current. The metallic silver once deposited is dissolved in the electrolyte by applying a reverse current, that is, an electric current from the electrode 1 to the electrode 2, and is further deposited on the surface of the electrode 1. When all the silver is dissolved from the surface of the electrode 2, the voltage-current relationship returns as shown by the solid line in FIG. Therefore, the device is capable of writing and erasing stored contents. However, when reading the contents, since a current flows from the electrode 2 to the electrode 1, the silver on the surface of the electrode 2 is gradually dissolved even if the amount is very small. If the dissolution is repeated, the stored contents on the surface of the electrode 2 will be erased. Therefore, in order to avoid this, it is sufficient to return the state by applying a reverse current after reading. . In this way, the contents of memory can be preserved semipermanently.

As shown in FIG. 7, the amount of current sufficient for changing the electrical characteristics, that is, the amount of current required for writing is proportional to the area of the electrode 1. Therefore, this device becomes more advantageous as the integration degree increases and the electrode surface becomes smaller. The write current amount needs to be larger than the read current amount, and it is desirable to take at least twice the read current amount, usually 10 times or more, in order to ensure the accuracy of the operation. The amount of current required for reading does not have to be as large as that for writing, and therefore this element is suitable for applications where reading is more frequent than writing.

Further, when many elements are arranged on the lattice, current may flow bypassing other elements even if the elements are not in the ON state. For example, in FIG. 8A, when P ₁₁ is in the OFF state but other elements are in the ON state, when a voltage is applied between b ₁ and a ₁ , b ₁ ⇒P ₂₁ ⇒ a ₂ ⇒ P ₂₂ ⇒ b ₂ ⇒ P
_The current flows in the order of ₁₂ ⇒ a ₁ , making it indistinguishable from the ON state. In order to prevent this, a pn junction is formed on the surface of the electrode 2 to form a Zener diode as shown in FIG.
You can do like (b). FIG. 9 shows an example of a memory element having a diode, in which the semiconductor layer 7 has a polarity opposite to that of the semiconductor electrode 2, and here a p-type semiconductor is shown. In this diode, the current flowing in the case of writing is opposite to that in the case of erasing, so it is necessary to use a Zener diode in which a current flows in the reverse direction at a certain value or more. Of course, the electrode surface of the electrode 2 may have a multi-layered structure to separate the electrode from the diode, or the diode may be formed on the electrode 1.

Actually, the surface of four electrodes 2 of 2 × 2 is 100
When a memory element assembly as shown in FIG. 1 having a cross-sectional area of μ × 100μ was made and silver was deposited by applying a current of 5 μAsec to each memory element, it was possible to clearly distinguish the change in resistance value between each element. It was

[0036]

The storage element of the present invention not only provides a storage device having a simple structure and a high degree of integration, but also retains its stored contents even when the power is turned off. Further, the stored contents are magnetically stable and can be read at high speed.

[Brief description of drawings]

FIG. 1 is a partially enlarged plan view showing an example of a storage element.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a partially enlarged plan view showing another example of the storage element.

FIG. 4 is a sectional view taken along line BB in FIG.

FIG. 5 is a cross-sectional view of FIG. 1A-A showing an example of manufacturing a memory element, and i) to iv) show the order.

FIG. 6 is a cross-sectional view of FIG. 1B-B showing an example of manufacturing a memory element, and i) to iv) show the order.

FIG. 7 is a graph showing voltage-current characteristics when a metal is deposited in a memory element (dotted line) and when metal is not deposited (solid line).

FIG. 8 is a circuit diagram of a case (a) without a diode of a memory element and a case (b) with a diode.

FIG. 9 is a cross-sectional view showing an example of the present invention having a diode.

[Explanation of symbols]

 1 Electrode 2 Electrode 3 Insulating Film 4 Electrolyte Layer 5 Precipitated Metal Layer 6 Substrate 7 Semiconductor Layer

Claims (2)

[Claims] 1. A memory using a chemical reaction, characterized by comprising a pair of electrodes and an electrolyte layer between them and in contact with both electrodes, wherein recording is performed by an electrochemical reaction accompanied by a change in electrical properties. element. 2. A memory element using a chemical reaction according to claim 1, wherein the electrochemical reaction is deposition of a metal on the semiconductor electrode and the change in electrical property is a change in electrical conductivity.